The implement hydraulic systems on earth moving, construction and mining vehicles generally use multiple variable and fixed displacement piston hydraulic pumps. For example, on a wheel loader during bucket lift, nearly all flow from implement pumps is directed to the lift cylinders to raise the bucket. These hydraulic piston pumps provide the power to move the implements on such vehicles. In the event of a catastrophic pump failure, debris from the failure may enter the implement hydraulic system and contaminate the system valves, cylinders and lines. Debris may also migrate back to the hydraulic tank and reenter the implement pumps, initiating subsequent pump failures. Many vehicles do not use full-flow return filtration due to very high cyclical return flow rates, the large filter size required to handle the large flow rates, and subsequent higher ongoing filter maintenance cost. Pumps on many vehicles generally do not use inlet filters or screens due to the potential for (a) cavitation damage from the inlet pressure drop caused by partially restricted filters or screens and (b) the ingestion of plugged screens or filters by the pump, which may result in instant catastrophic pump failure.
A catastrophic pump failure requires significant system disassembly for debris removal and cleaning to reduce the probability of additional pump failures caused by debris in the system. These failures are very expensive in terms of repair costs and machine downtime. The only way to prevent a catastrophic pump failure is to detect a pump that is starting to fail and to replace it.
However, knowing when a pump is starting to fail is very difficult to detect in a system with multiple pumps. There is currently no method of detecting pump failure during normal machine operation. The only available methods to measure pump performance require the machine to be stopped and test equipment to be installed in the machine. One such method involves the installation of a flow meter and the measurement, while the machine is being serviced, of pump outlet flow under maximum pressure conditions. This method is rarely used because the necessary test equipment is large and labor intensive to install and remove. A second method involves the performance of a case drain (bucket test) during machine servicing. This test measures leakage flow from the pump case back to the tank with the pump in a maximum pressure stall condition. However, because hydraulic piston pumps may go from normal operation to failure in a matter of hours, the probability of finding a pump that is about to fail is very remote with either of these methods.
If impending pump failure could be detected early, the pump could quickly and easily be replaced without contaminating the system and causing significant downtime. This would result in a significant reduction in warranty costs, repair-hours and machine downtime, while improving machine reliability and availability.